Neurotransmitters in carotid body function: the case of dopamine--invited article

The carotid body (CB) is the main peripheral chemoreceptor. The present model of CB chemoreception states that glomus (type I) cells are the primary receptors, which are synaptically connected to the nerve terminals of the petrosal ganglion neurons. In response to hypoxia, hypercapnia and acidosis, glomus cells release one (or more) transmitter(s) which, acting on the nerve terminals of chemosensory neurons, increases the afferent discharge. Among several molecules present in glomus cells, dopamine, acetylcholine and 5'-adenosine-triphosphate have been proposed to be the excitatory transmitters in the CB. Beside these putative excitatory transmitters, other molecules modulate the chemosensory process through direct actions on glomus cells and/or by producing tonic effects on CB blood vessels. In this review, we focus on the role played by dopamine in the CB chemoreception, with emphasis on the open question if the reported differences on its actions on the generation of afferent chemosensory activity reflect true species differences. The available data suggest that dopamine may play a modulatory role within the cat CB, while in the rabbit CB, dopamine is an excitatory transmitter. Therefore, the reported differences on the actions of exogenously applied dopamine and its participation on the generation of afferent chemosensory activity appear to reflect true species differences.